How to implement an automated render farm with remote access?
If they are connected to the internet, try Sheepit. If you run their client on each computer they will render for the farm and if you upload a project it will first be rendered on your own hardware so easy to setup, everybody wins. Unless 500MB file size limit is too little for your scenes and you want to use exr output with passes and render layers instead of only png that Sheepit supports. But it has the advantage of being very easy to set up.
If I am not mistaken, some of their software used for the farm is open source as well, so it's worth exploring if it may be possible to use it to setup your own farm as well.